Bug 89617 - FcConfigAppFontAddFile() returns false on any font file

Prior to the change of 32ac7c75
FcConfigAppFontAddFile() always returned FcTrue no matter what
fonts was added. after that, it always returned FcFalse because
adding a font doesn't add any subdirs with FcFileScanConfig().
so changing that to simply ignore it.
Also fixing it to return FcFalse if non-fonts was added, i.e.
FcFreeTypeQuery() fails.
https://bugs.freedesktop.org/show_bug.cgi?id=89617